Electric-wave transmission system



Patented June 11, 1929.

UNITED STATES PATENT OFFICE.

FRANCIS X. RETTENMEYER, OF MONTCLAIR, NEW JERSEY, ASSIGNOR TO -WESTEBNELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION ,OF

NEW YORK.

ELECTRIC-WAVE TRANSMISSION SYSTEM.

Application filed October 20, 1925. Serial No. 63,575.

This invention relates to electric wave transmission systems, and moreparticularly to systems for transmitting binaural effects.

It is well known that a listener determines the location of sound atleast in part by virtue of the difference in intensity and thedifference in phase of the sounds reaching his two cars.

From this discovery it was also found that by providing, at a pick-uppoint, speech transmitters separated a distance approx1-' mately equalto the distance between the ears of a human being and by connecting thetransmitters to separate telephone rcceivers, binaural or locationeffects couldtransmitted to a distance.

It has further been disclosed that binaural effects may be transmittedby radio by sup plying the waves from the separate pick-up transmittersto two individual radio transmitters operating on different carrierfrequencies, or wave lengths, with separate radio receivers. I

The present invention constitutes an improvement over prior knownsystems and has for an object the transmission of binauml or locationeffects by means of a single carrier frequency wave or channel.

Another object is to transmit binaural efiects over a multiplexsignaling circuit by means of a single carrier frequency wave.

A further object is to transmit binaural efiects by means of separateside-bands of va common carrier frequency wave. I A feature of theinvention is a multiplex carrier current system for transmitting binaural effects over wires by means of a' single carrier frequency wave.

Another feature is a system operating on the successive modulationprinciple for transmitting binaural effects by radio on a single wavelength or carrier frequency wave.

This invention provides novel means for utilizing electric waves for thetransmission of binaural or location effects. The means provided isadapted to permit waves from separate pick-up transmitters, spaced aparta suitable distance, for example, having a separation about equal tothat of the human ears, to separately modulate the same car.- rierfrequency wave. Suitable filters are adapted to effect a selection ofone side-band from one wave modulation and the opposite side-band fromthe other wave modulation, which side-bands may be transmitted togetherwith an unmodulated carrier frequency component, over a wire line. Atthe receiving end, other filters are adapted to separate'the side-bandsinto two receiving channels including associated detectors and telephonereceivers for reproducing the sounds impressed upon the pick-uptransmitters.

If a listener applies the telephones to his ears a true impression ofthe location of the original sounds is received, because the soundsreceived in his' two ears have substantially the same difi'erence inintensity and phase as the original sounds at the two pfck-uptransmitters.

In another application of the invention, adapted for radio transmissionof binaural effects, the side-bands selected from the first modulationsmay be caused to modulate a radio frequency carrier wave. Means isprovidedto select the opposite side-bands respectively of each of thesecond modulations and also an unmodulated component, having the properfrequency to enable detection of the side-bands. The selected waves mayif desired be amplified and supplied to an antenna.

A receiving station including a selective network and radio frequencydetector, two separate receiving channels each comprising individualfilters, detectors, and receiving devices, is adapted to receive thetransmitted waves and to derive therefrom separate sound waves conveyingthe binaural effect.

The invention is illustrated in the attached drawings wherein:

Fig. 1 shows a wire binaural transmission system. I

Fig. 2 shows a binaural radio transmitting system.

Like reference characters have been used throughout the figures of thedrawings to indicate like parts.

The system of Fig. 1 includes the separate pick-up transmitters 10adapted to supply currents-corresponding to sound waves to themodulators 11 which are supplied from a common source with a carrierwave of frequency suitable for transmission over a wire line. Themodulators ,11 may be of any well-known type preferably employing spacedischarge tubes, such, for example, as is described in Patent 1,350,752to Van Der Bijl, August 24, 1920. The source 12 is preferabl a spacedischarge oscillator of any wellown form. The modulating devices 11 havetheir output terminals connected to respective filters 13 and 14. Thesefilters may be of any well-known type designed to pass waves includedwithin a desired band and to exclude waves outside this band. Filters ofthis type are described in Patent 1,227,113 to Campbell, Ma 22, 1917.More specifically, filter 13 is pre erably designed to pass the upperside-band component of the modulated wave produced by the associatedmodulator 11. and filter 14 is preferably designed to pass the lowerside band component of the modulated wave produced by the modulatorassociated with it. Each filter mayalso pass a wave component of thecarrier frequenc All other waves are preferably exclu ed bythesefilters.

The filters 13 and 14 both have their output terminals connected to theinput terminals of an amplifier 15, which may be of any well-known typebut preferably employing space discharge .tubes. An amplifier of thistype is disclosed in Arnold Patent 1,448,550, "March 13, 1923. Anotherbandpass filter 16 is connected between the output terminals ofamplifier 15 and a wire line Any number of other signal channels such as18 and 19 may also be connected to .the

wire line 17 at the points indicated.

The filter 16 is of the well known bandpass type and is preferablydesigned to transmit the side-band components and the unmodulatedcomponent of carrier frequency selected by filters 13 and 14, whichcomponents constitute the frequencies assigned to the binaural channel,and to exclude any waves having frequencies corresponding to thefrequencies assigned to the channels 18 and 19.

The wire line 17 is connected at itsreceiving end to a second channelfilter 20, adapted to pass waves assi ned to the binaural channel and toexclu e waves assigned to the channels'18 and 19. The output terminalsof filter 20 are connected to sepa rate branches of the receivingcircuit, which branches include separate filters 21 and 22, se aratedetectors 23 and 24, and separate te ephone receivers 25 and 26.

The filters 21 and 22 are adapted to select the respective side-bands ofthe binaural channel and to supply these side-bands to the respectivedetectors 23 and 24. The filters 21 and 22 may be identical with thefilters 13 and 14, respectively. The detectors 23 and 24 may be of anydesired type such terminals of filters 21 and 22 or filter 20.

Channels 18 and 19 may be used to transmit binaural signals, telephoneorv telegraph messages.

When the system ,of Fig. 1 is in operation, thetransmitters 10 areseparated by a distance suitable to the production of binaural effects.In the simplest case this of a listener located at the same point. The

waves from transmitters 10 are supplied through respective transformers27 to the input circuits of the modulators 11. The modulating devices 11cause the-carrier wave from the source 12 to be modulated in accordancewith the waves from transmitters 10 and cause the modulated waves to betransmitted to the filters 13 and 14 respectively. As already stated,filter 13 transmits the upper side-band and attenuates the lowerside-band, whereas filter 14 transmits the lower side-band andattenuates the upper side-band. Both filters transmit the carrierfrequency waves.- Consequently, the upper side-band of one modulationand the lower side-band of the other modulation, with an unmodulatedcarrier com onent, after being amplified by the ampli er 15, aretransmitted through the filter 16 to the line 17 to constitute a carrierwave adapted to produce binaural effects at the receiving station.

The binaural carrier wave may be transmitted over the line 17simultaneously with other signals, consisting of carrier modulatedwavesor unmodulated-waves, transmitted over the separate channels 18 and 19.border to separate the two side-bands from waves corresponding to theother channels, the filter 20 is provided. This filter transmits .theside-bands of the binaural channel and attenuates the waves assigned toother. channels. In the branch receiving circults, filter 21 selects theupper side-band, whereas filter 22 selects the lower side-band of wavestransmitted by filter '20. These devices 23 and 24, respectively, andyield sound waves having the characteristic difference in intensity andphase of the original sounds at the transmitters 10 provided the totalphase shift in each transmitting branch and each receiving branch isidentical. If necessary or desirable, phase shifting devices 50 and 51may be inserted in the respective transmitting branches to bring aboutthe required hase displacement. One of these phasejshifters may however,be omitted, again either or both may be included in one or both of thebranches be-' tween the detectors 23 and 24 and the receivers 25 and 26.Furthermore, the may be introduced at any other point in t e circuits,for example, they may be associated with the filters 13, 14 or 21 and22.

Phase shifting circuits being well known, it is believed unnecessary todescribe them in detail since any suitable arrangement for this purposemay be used.

A listener'by applying the telephone receiver 25 to one ear and thetelephone receiver 26 to the opposite car, will receive an impression ofthe location of the source' of sound waves relatively to thetransmitters In Fig. 2 a system for binaural broadcasting by radio isillustrated. The portion of this system to the left of the dotted line1-1 is like the corresponding portion of Fig. 1 on the left of thedotted line 22 with the omission of phase shifters 50 and high frequencywave is combined with and modulated in accordance with the selectedside-band. A band filter or selective network 32 of any well known t peis connected to the output terminals 0 modulator 30 and is adapted toselect one side band, for example, the lower side-band of the modulatedwave produced by the modulator 30 and also to select an-unmodulatedcompo nent having a frequency represented by the sum or difference ofthe carrier oscillations supplied by sources 12 and 31. The fi lter 32is designed to attenuate waves above or below the range including theselected sideband and carrier component. The selected waves transmittedby filter 32 are supplied to the amplifier 33 which may be a poweramplifier employing space discharge tubes and arranged in any one ofmany well.

known manners. The output circuit of amplifier 33' is coupled to anantenna 34.

A radio receiving circuit including an ancluding filters 21 and 22',detectors 23 and a 24' and telephone receivers 25 and 26. A source ofoscillations, for enabling detection of the received waves is connectedto the detector. This source preferably supplies waves of the samefrequency as source 31. The filters 21' and 22' may be in general likethe filters 21 and 22, respectively, of Fig. 1 and designed to transmittherespective upper and lower side-bands derived from t e radiofrequency waves by detector 23". The detectors 23' and 24' may be ingeneral, like the detectors 23 and 24.v

In the operation of the circuit of Fig. 2, the transmitters 10 aresupplied with sound waves having frequencies, for example, includedwithin the range from 0-5 kilocycles. The carrier .wave source 12 may bedesigned to'supply oscillations of 60 kilocycles. The filter 13 maytransmit waves within the band of substantially 60 to kilocycles,whereas filter 14.may transmit waves within the band of 55 to 60kilocycles. The high frequency carriersource 31 may su ply oscillationsof 1000 kilocycles and tl ie band filter 32 may be designed to transmita band of waves from 935 to 945 kilocycles.

This latter range of frequencies includes the lower side-bandtransmitted from the modulator 30 and also the frequency of anunmodulated component represented by the difference in frequency of thetwo carrier sources 12 and 31.

The side-band and unmodulated carrier waves received by antenna 35 aresupplied to detector 23". From the combination of waves from the source31' with the sideband waves, there are produced waves constitutingside-bands of 55 to 60 kilocycles and 60 to 65 kilocycles, and from thecombination-of waves from the source 31 with the unmodulated componentof carrier frequency, there is produced a carrier component of 60kilocycles. The filters 21'- and 22 select these respective side-bandstogether with a certain amount of the unmodulated component of-60kilocycles and supply these waves to detectors 23' and'24 respectivelyfrom which are derived the respective signal waves for actuating thereceiving devices 25 and 26.

An advantage of the invention herein described is that by transmittingsignals as modulations of a single carrier frequency wave, asdistinguished from prior arrangements wherein a plurality of channelsemploying different carrier frequency waves are required, the number ofchannels in a given system within a given frequency band may bematerially increased, the system may be greatly simplified, and the costof construction and operation materially reduced.

The arrangement described also possesses the advantage that thefrequency range required for binaural transmission is substantially thesame as that used for broadcasting, namely 10 kilocycles. Moreover,ordinary signals can be reproduced from the transmitted waves by usingan ordinary heterodyne radio receiver. The signal waves with binauraleffects can be produced 'from the same transmitted waves by merelyremodeling the receiver to provide se arate circuits for selecting anddetecting t e in-' termediate frequency waves.

What 1s claimed 1s:

1. In a multiplex system adapted to transmit binuaral effects, twopick-up transmitters, two receiving devices, a line extending betweensaid transmitters and said devices and adapted to transmit wavesassigned to a plurality of signal channels, means for causing thereproduction of sounds at said separate receivers having thecharacteristics of the sounds impressed upon said separate transmitters,comprising a source for a car rier wave, means for separately modulatingsaid carrier wave by audio frequency waves from both of saidtransmitters and means comprising a' filter for exclusively transmit--ting said carrier wave and the two side bands to the line.

2.In a multiplex system, a transmission line adapted to transmit wavesassigned to a plurality of signal channels, a binaural pick-up systemincluding separate transmitters of audio frequency waves, means toexclusively transmit to the transmission line a carrier wave having theside bands thereof respectively modulated'by waves from saidtransmitters, a binaural receiving system in cluding separate receivingdevices connected to said line, and filters for separating wavesassigned to the binaural channel from Waves assigned to other channels.

3. In a binaural transmission system, means for producing two electricwaves within the same frequency range having the characteristics ofsound waves at two points in space, means for producing two side bandscorresponding to a single carrier frequency wave modulated by both saidfirst mentioned waves, a wire line for transmitting said sidebands to areceiver, a filter at the receiving end of said line for separating thewaves assigned to the binaural channel from waves assigned to otherchannels, said receiver comprising means for separately deriving, fromsaid side bands, signal waves having the characteristics of the originalsound waves.

4. In a multiplex transmission system, a binaural transmitting stationhaving means for producing two electric waves within the same frequencyrange, means for separately modulating a single carrier Wave, with saidtwo electric Waves, a binaural receiving station, a line, meanscomprising a channel filter for exclusively transmitting to the linebetween said stations, said carrier wave of single frequency and twoside bands derived therefrom, whereby hinaural effects may be producedat said receiving station.

5. In a multiplex system for transmitting binaural sound effects, twopaths transmitting waves within the audiofrequency range, a common lineconnected to said paths, two

receiving paths also connected to said line,

means for separately modulating a single carrier wave in accordance withthe a'udio frequency waves in the two transmitting paths, and means forexclusively transmitting to said receiving paths said carrier waveseparately modulatedcin accordance with the waves transmitted over saidtwo transmitting paths.

6. In a multiplex system the method of binaural signaling whichcomprises, deriving two waves from a source of sound, separatelymodulating a carrier wave by said two waves to produce two modulatedwaves, sepa rately selecting opposite side bandsof said modulated waves,transmitting said selected side hands over a wire line and filteringsaid waves from waves assigned to other channels 7. In a multiplexsystem for binaural transmission and reception, the method whichcomprises producing a single carrier wave, separately modulating saidcarrier wave with two separate signal audio frequency waves representingsounds having.

binaural characteristics, impressing said modulated carrier wave andwaves of other frequencies in a common restricted path, selectivelyreceiving said modulated wave and deriving therefrom said separatesignal waves to reproduce sounds having binaural characteristics.

8. In an electric wave transmission system, a sound source, a pluralityof sources of signal waves spaced different distances from said soundsource, means for separately modulating a carrier wave by signal wavesfrom said sources to produce two modulated waves, means for changing thephase rela: tion of the modulated-waves, means for selecting oppositeside-band components of the modulated waves, and means for. transmitting said side band components to a receiving device.

9. In a multiplex binaural transmission system, means for producing twosets of electric waves within the same frequency range and having thecharacteristics of sound waves at two points in space, means forproducing two side-bands. corresponding to a my name this 6th day ofOctober, A. D. 1925.

FRANCIS X. RETTENMEYER.

